These descriptions relate generally to circuit elements that attenuate oscillating electrical signals in predetermined frequency ranges, and more particularly to band-stop filters useful, for example, in cable-television networks and other applications where multi-frequency signals are transmitted and predetermined ones of the signals are to be blocked.
In a typical cable television (CATV) network, a head-end facility generally broadcasts a variety of programs in a number of respective frequency channels. At the user end of the network, users selectively tune their television units and other media devices to particular frequency channels to receive particular programs. In many such networks, particular ranges of channels are dedicated to particular subscription contracts or tentative pay-per-view arrangements. For example, premium programming selections, for which extra payments are required, may be exclusively provided on dedicated ranges of frequency channels. Accordingly, users can optionally decline to view particular ranges of channels. Operators of such a network are thus challenged to block declined programs from being viewed by particular users. Without such enforcement, many users would likely view premium programming while declining to pay the associated fees. Accordingly, many band-stop filters are available for blocking selected channels ranges and permitting channels ranges above and below the selected ranges.
The advent of digital programming in CATV networks has given rise to challenges in blocking selected frequency ranges while permitting passage of signals in frequencies near the blocked ranges. Reduced insertion loss and increased return loss are desired in frequencies to be passed. Insertion loss refers to energy losses as a signal traverses a circuit. Return loss refers to the attenuation of signal reflections, which propagate back toward the source of a signal, as a signal traverses a receiving circuit. Improved attenuation is desired in any frequency range selected to be blocked. Currently available filters used in the CATV industry exhibit insertion-loss and return-loss performances that are unacceptable in some applications. It is believed that parasitic circuit effects and inductive couplings, such as magnetic field couplings, among filter components contribute to the failures of the available filters. Thus, improved band-stop filters are needed at least to meet the current challenges in the CATV industry.
Therefore, filters having improved insertion-loss and return-loss performances in CATV frequency ranges are desired. Accordingly, improvements in circuit elements and arrangements thereof are needed toward minimizing or at least reducing the mutual couplings among the components of band-stop filters.